The manufacture of an integrated circuit device requires the formation of various layers (conductive, semiconductive, and non-conductive) above a base substrate, such as a silicon substrate, to form necessary components and interconnects. During the manufacturing process, a layer or a portion of a layer is removed to planarize or form the various components and interconnects. Chemical-mechanical polishing (xe2x80x9cCMPxe2x80x9d) is a well-known technique for removing materials on a semiconductor wafer using a polishing device and a polishing agent. The mechanical movement of a polishing surface (e.g., a polishing pad) of the polishing device relative to the wafer in combination with the chemical reaction of the polishing agent provides an abrasive force with chemical erosion to planarize the exposed surface of the wafer or a layer formed on the wafer.
CMP polishers can incorporate various monitoring techniques to detect a removal of a layer of a semiconductor wafer during polishing. Such monitoring can be used to determine the end point of the polishing process. One type of detection technique uses a visible light beam. During the polishing process, a window or hole in the polishing platen passes over an in-situ monitor, which takes a reflectance measurement indicative of the end point of the polishing process. In this type of system, the visible light is directed to the front side of the semiconductor wafer (the side of the semiconductor wafer being polished) through a hole or window formed in the polishing surface. One disadvantage associated with these systems is that the accuracy of the optical monitoring can be reduced if slurry fills the hole formed in the polishing surface or if the window in the polishing surface becomes scratched during the polishing process.
There is a need, therefore, for a method and system for detecting an exposure of a material on a semiconductor wafer during chemical-mechanical polishing.
The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims.
By way of introduction, the preferred embodiments described below include a method and system for detecting an exposure of a material on a semiconductor wafer during chemical-mechanical polishing. The semiconductor wafer comprises a first surface and a second surface. A first material is exposed at the first surface and underlies a second material. In one preferred embodiment, a light source transmits light at the second surface of the semiconductor wafer during the polishing of the first surface of the semiconductor wafer. The second material at least partially allows the transmitted light to reach the first material, and the first material at least partially reflects the transmitted light. The amount of light reflected from the semiconductor wafer is monitored by a detector, and the change in the amount of reflected light indicates an exposure of the second material at the first surface of the semiconductor wafer. Instead of being opposite the second surface of the wafer, the light source and detector can be positioned opposite the first surface of the wafer. Alternatively, the wafer can be positioned between the light source and the detector. Other alternatives are described herein.
The preferred embodiments will now be described with reference to the attached drawings.